I. Field of the Invention
This invention relates to a process for manufacturing manifolds for a vehicle engine and, in particular, to applying a ferritic nitro carburization process to the flanges of the manifold to prevent corrosion in humid environments.
II. Description of the Prior Art
Vehicle engines incorporate manifolds for directing particular gasses through predetermined passageways. An engine exhaust manifold includes tubular arms in communication with the exhaust ports of the engine and a collector chamber in communication with the arms and the exhaust of the vehicle. Exhaust gasses from the engine flow through the arms to the collector chamber and then directed through the exhaust system including the catalytic converter.
While the body of the manifold may be cast, stamped or even hydroformed into the desired configuration, flanges are attached to the ports of the manifold to facilitate mounting to the engine and exhaust system. The flanges include a machined face to sealingly connect to the engine and a plurality of apertures to receive stud fasteners. However, these carbon steel flanges which are typically welded to a stainless steel manifold body are prone to corrosion particularly when stored in humid environments. While a minimum amount of rust will not inhibit performance of the manifold, the appearance of the rust gives the appearance of a defect and is typically cleaned off before mounting to the engine.
The present invention overcomes the disadvantages of the prior known exhaust manifolds by providing a process of carburization of the manifold flanges to prevent corrosion.
The vehicle manifold of the present invention includes a body configured to fit within the engine compartment while directing exhaust gasses from the exhaust ports of the engine to the exhaust system. The body will include a collector chamber and a plurality of tubular arms corresponding to the exhaust ports. The arms are designed to communicate with the exhaust ports and direct the exhaust gasses to the collector chamber which is then directed to the exhaust system. Welded to the ports of the arms and the collector chamber are flanges for connecting the manifold to the engine. In a preferred embodiment, the manifold body is fabricated from stainless steel and the flanges are carbon steel. Apertures in the flanges receive stud fasteners to secure the manifold to the engine.
Prior to the attachment to the manifold body, the flanges are treated with a corrosion resistant material. In a preferred embodiment, the flanges are subjected to a ferritic-nitro carburization process nitrogen-based penetrant to infuse into the surface of the flange. This penetrant bonds with the existing oxides in the carbon steel flange to prevent the oxides from boding with the iron to form iron-oxide. Although alternative rust inhibitors are available, the ferritic nitro carburization process does not inhibit welding of the flanges to the manifold body and does not wear off in humid environments.
Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings.